This invention relates generally to adjustment apparatus for transducers used for detecting indicia on a moving surface and, with greater particularity, to flexure apparatus for enabling improved accuracy and convenience in adjusting the relationship between an encoded disk on the shaft and the transducing device sensing the disk indicia.
The motion or position of rotating shafts are usually detected by sensing recorded indicia on disks on the shafts that effect a change in the transmission of light or intensity of magnetic flux as the disks move past stationary sensing transducers that typically produce electrical output signals whose amplitude is in proportion to the transmitted light or magnetic field. To sense smaller and smaller increments of motion, represented by correspondingly finer indicia, it is necessary to detect these recorded indicia by careful and stable adjustment of the transducing devices relative to the rotatable disks. The output signals representing the recorded indicia must be reproduced with optimum definition to enable the desired and necessary accuracy.
Adjustment of the position of a non-rotating, stationary transducing device or its optical aperture relative to its disk requires consideration of several factors: to maximize signal strength from the transducer or sensing device, the adjusted transducer or aperture must remain at the same radius from the center of the rotating shaft as the centerline of the disk indicia; during changes in position an adjusted transducer or aperture must be moved by uniform forces to avoid irregular changes in position; the transducer or its aperture should be isolated from variable external forces encountered during the adjustments; the adjustment mechanisms are preferably insensitive to temperature changes and external vibration during operation; and adjustment mechanisms should be made of few components for accuracy, reliability and minimum expense.
Techniques of achieving the proper relationship between a disk and transducer encompass several approaches. A coarse technique often used varies the disk position by hub movement; in U.S. Pat. Nos. 4,033,833 and 4,476,457 the disks are positioned with uncertainty by loosening set screws and moving the disk hubs, while in U.S. Pat. No. 4,289,962 disks are selectively rotated against frictional restraint. Better accuracy is obtained, however, by adjusting the transducer support. Examples are shown in U.S. Pat. Nos. 3,894,232 and 4,031,444 and in "Leadscrew Emitter Phase Adjustment," R. B. Schuman, IBM Technical Disclosure Bulletin, Vol. 21, No. 4, pg. 1531, Sept. 1978. In these, multiple piece mechanisms have been devised that permit finer changes in the transducer support position. These devices maintain the necessary constant radial dimension but require multiple components and assembly and are subject to displacing forces during adjustment and to positional uncertainty due to bearing clearances.
Another adjustment technique has been the use of flexure members that provide a smoother transition between positions. This method has been often used to obtain the required positioning of magnetic transducers because of the ease and rapidity with which banks of transducers can be properly located. Such arrangements are shown in U.S. Pat. Nos. 2,859,084 and 3,936,882 and in United Kingdom Pat. No. 784,572. Although of simpler construction, the mechanisms have not been devised for optical transducers nor maintenance of radial dimension, protective isolation from disturbing forces, and insensitivity to differential coefficients of expansion.